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Android Plugin for Gradle, featuring ProGuard and Scala support

This is the Android plugin for the Gradle build system. This plugin enables the creation of Android applications using Gradle, with all of the power and flexibility you’ve come to expect from Gradle, plus support for ProGuard and Scala.

The Android plugin fully integrates into the Gradle build lifecycle by extending the Java plugin. Furthermore, the incorporation of ProGuard into the build not only ensures that Android application packages are small and tight, it also trivially enables the use of Scala for Android application development simply by incorporating the existing Scala plugin into the build. ProGuard will include only those classes from the Scala library that are actually used by your Android application, resulting in an application package that is as small as possible.

Tasks and Lifecycle

The Android plugin adds the following tasks and dependencies to the build:

Task

Description

Depends On

Dependents

androidProcessResources

Generate R.java source file from Android resource XML files

compileJava

proguard

Process classes and JARs with ProGuard (by default, this task is disabled, more on this below)

jar

androidPackage

Creates the Android application apk package

proguard

androidSignAndAlign

Signs (with a debug or provided key; more on this below) and zipaligns the application apk package

androidPackage

assemble

androidInstall

Installs the debug package onto a running emulator or device

assemble

androidUninstall

Uninstalls the application from a running emulator or device

androidEmulatorStart

Starts the android emulator

androidInstrumentationTests

Runs an instrumentation test suite on a running emulator or device

androidInstall

Usage

To use the Android plugin for Gradle you must first create the application skeleton using the android command-line tool. For example:

This will create and Android application skeleton that you can immediately build using Ant. To build with Gradle instead, you must (1) create a build.gradle file that includes the Android plugin, and (2) either move the source code to the directory expected by Gradle, or tell Gradle to use the src directory of your project directly.

1) Create a build.gradle file in the root directory of the project, and include the Android plugin as follows:

2) The android create project command created the source code directly in the src directory of the project. The Android plugin tries to conform to the conventions established by Android’s Ant-based build, but in this case it is better to conform to Gradle’s “source sets” convention, since it allows you to have separate test source code, or to use multiple languages. Therefore, we recommend that the source should be moved to src/main/java instead. Once you’ve done this you can, of course, utilize Gradle’s source sets to their full extent by placing resources in src/main/resources, Scala source files in src/main/scala etc. However, if you prefer to keep your source code directly in the src directory (for example, if you need to retain compatibility with Ant) then you can do so by configuring the Java source set in your build.gradle file. Just add the following to build.gradle:

sourceSets {
main {
java {
srcDir 'src'
}
}
}

If your Android project was initially created by Eclipse rather than the android create project command, then you will have some additional setup work to do. The Android plugin for Gradle must be told the location of the Android SDK. When you create a project with the android create project command, the location is filled in for you by the application generator, but the Eclipse project generator does not provide this information to the project. Therefore, you must fill it in yourself. To do this, create (or edit) the local.properties file in the root of the project and add the sdk.dir property, referring to the location of your Android SDK installation:

sdk.dir = /path/to/android/sdk

Note that this file should not be checked in to your version control system as it will likely differ across various development environments. Alternatively, you can use the ANDROID_HOME environment variable instead.

Once you’ve performed these steps you can build your Android application by invoking the tasks described above.

This build script configures the build to sign with a provided keystore. This configuration applies for every build (1). It also sets Gradle to expand properties in every resource file (2).

In this way you can get a full build with the command:

gradle assemble

It processes all the resources, expanding them with properties from the project’s scope, compiles classes, packs them into the dex file, builds the apk, signs it with the provided keystore (but does not process it with proguard) and zipaligns the package, which is named -x.y.z.apk and placed in /build/distributions. You can see the proguard task is skipped from Gradle’s output during the build.

You can create several build configurations and choose which one to execute from the gradle command line. The task configureDebug (3) defines the Gradle classifier for the package name. Executing this build with the command:

gradle configureDebug assemble

creates a package with same steps than the default build, but the package name is project-x.y.z-debug.apk.

The task configureRelease (4) defines a release configuration task, which activate the proguard step. Again, you get the package named -x.y.z.apk in the same output directory.

To disable signing and get a signed apk with the debug key, you can remove the androidPackage configuration (1): if keyStore or keyAlias are null, the signing is skipped and the debug key is used. Of course, you can put the signing configuration in a dedicated configuration task and invoke that task in order to get a signed package (or not to call it for the debug signed package).

Also note that if you don’t supply password (that is, keyStorePassword or keyAliasPassword are null), Gradle asks for them on the command line (not very good for CI servers…).

To install the generated apk onto a running emulator or a device connected with USB (and configured in debug mode), run:

gradle androidInstall

This installs the default built package; as with previous examples, if you want to install the debug (or release) package, you have to issue:

gradle configureDebug androidInstall

or

gradle configureRelease androidInstall

The androidUninstall task uninstalls the application from a running emulator or a device. There is no need to specify which package: there can be only one package to undeploy and it’s defined by the base package name of the application, from androidManifest.xml.

Eclipse

You can use Gradle to generate an Eclipse project for you. The Android plugin enhances this process by setting up the Eclipse project correctly for Android, which includes establishing the correct class path and inserting the Android builders into the build process.

To use the Eclipse integration, first make sure that you apply the Gradle Eclipse plugin in your build.gradle file:

apply plugin: 'eclipse'

Then you can generate the Eclipse project files as follows:

gradle eclipse

Instrumentation Tests

The plugin is able to run instrumentation tests for you on a connected device or emulator:

gradle androidInstrumentationTests

On projects that do not define any instrumentations in their manifest, this task will safely be skipped. By default, the task runs all tests in the given project, using Android’s default test runner. If you want more control, you can add a configure closure to your test project:

The ‘run’ method can you be used in different ways. If used as above, all tests will be run using the given test runner. The ‘options’ field can be used to route parameters to the Activity manager that’s used to run the instrumentation (cf. ‘adb shell am instrument’). Note that you don’t have to supply the “-w” parameter, that’s done by default.

You can also partition your test suite to run with different runners. Note that this only works if you don’t also have a more general runner configured as seen above. Currently, the plugin allows you to partition by test package and annotation:

If your test project’s package ID is com.myapp.test, then this configuration will first run all test cases within the com.myapp.test.unit package with the com.myapp.test.MyUnitTestRunner, and then run all test cases carrying Android’s “Smoke” annotation in the same manner.

There is also limited support for publishing JUnit compliant test reports that can be read by build servers like Hudson. Currently, this only works if you’re using the Android JUnit test report runner or a sub-class of it: Android JUnit Report In that case, the test reports generated by that runner will be published to build/test-results. We plan to make this more flexible and configurable in future versions.

Start Emulator

For starting the emulator with gradle, you need do define the AVD-Name from your android-emulator in your build.gradle:

androidEmulatorStart {
avdName = "Main"
}

Limitations

In the current version of the Android plugin, the proguard task is not very configurable.

The androidManifest.xml file is not processed as a normal resource, i.e. there is no properties expansion (so, for example, you don’t get the version set in the version tag, you have to align them manually).